An antenna is a device that transmits and/or receives electromagnetic waves. In this regard, the antenna converts electromagnetic waves into an electrical current and converts electrical current into electromagnetic waves. Typically, the antenna is an arrangement of one or more conductors, which are oftentimes referred to as elements. To transmit a signal, a voltage is applied to terminals of the antenna, which induces an alternating current (AC) in the elements of the antenna, and the elements radiate an electromagnetic wave indicative of the induced AC. To receive a signal, an electromagnetic wave from a source induces an AC in the elements, which can be measured at the terminals of the antenna.
The design of the antennas typically dictates the direction in which the antenna transmits signals in a particular direction. Notably, antenna may transmit signals horizontally (parallel to the ground) or vertically. One common antenna is a vertical rod. A vertical rod antenna receives and transmits in a vertical direction. One limitation of the vertical rod antenna is that it does not transmit or receive in the direction in which the rod points, i.e., it does not transmit or receive vertically.
There are two types of antenna directional patterns: omni-directional and directional. An omni-directional antenna radiates equally in all directions. An example of an onmi-directional antenna is the vertical rod antenna. A directional antenna radiates in one direction more than another.
Antennas are oftentimes used in radio telemetry systems for system control and data acquisition (SCADA) applications, where a vertical rod antenna may not be desirable. In this regard, antennas may be used in traffic control security, irrigation systems, gas, electric, water and power line communications. In such exemplary systems, the antenna may be mounted in a location that would not be appropriate for normal length vertical rod antennas. Indeed an antenna used in such systems may need to be mounted in a position such that the vertical rod antenna would physically interfere with other equipment being used in the system.